Combination residue hydrodesulfurization and zeolite riser cracking process

ABSTRACT

A multiple stage hydrodesulfurization process is described for the catalytic hydrodesulfurization and hydrodemetallization of a residual petroleum oil boiling above the gasoline range followed by a zeolite riser cracking process. The product of the hydrodesulfurization section comprises essentially material boiling above the gasoline range and comprises little material boiling below the initial boiling point of the residual oil feed. The hydrodesulfurization-demetallization section comprises an initial stage involving relatively high hydrogen pressure in the presence of a catalyst comprising a relatively low proportion of catalytically active hydrogenation metals. The process employs a final hydrodesulfurization stage in series having a relatively lower hydrogen pressure and a catalyst comprising a relatively higher proportion of hydrogenation metals. The stream entering the final hydrodesulfurization stage contains an amount up to 10, 20 or even 25 weight percent of the asphaltene content of the charge to the first stage while the effluent from the final stage is essentially free of asphaltenes. The metals content of the final stage effluent is so low that said effluent can be charged without blending with a distillate oil to a fluidized zeolite riser cracking unit (FCC) to produce gasoline and fuel oil. The zeolite catalyst make-up requirement due to metals accumulation on the zeolite catalyst is no greater than zeolite make-up requirement when a distillate gas oil comprises the entire feed to the reactor. The sulfur content of the final stage effluent is so low that the sulfur dioxide content in the zeolite regenerator flue gas is able to meet commercial requirements and so that the fuel oil range product of the FCC operation is sufficiently low that the FCC fuel oil product also meets commercial fuel oil sulfur specifications without requiring further hydrodesulfurization, whereby all hydrodesulfurization can precede the FCC step and no hydrodesulfurization is required after the FCC step. Of course, further desulfurization can follow the FCC step, if such is desired for a specialized requirement.

United States Patent 1 Henke et al.

1 1 COMBINATION RESIDUE HYDRODESULFURIZATION AND ZEOLITE RISER CRACKINGPROCESS [75] Inventors: Alfred M. Henke, Springdale; Joel D. McKinney,Pittsburgh, both of Pa;

[73] Assignee: Gulf-Research & Development Company, Pittsburgh, Pa.

22 Filed: Aug.- 22, 1973 '21 App]. No.: 390,359

208/216, 208/309 [51] Int. Cl ClOg 37/00 [58] Field of Search 208/61,89, 210, 213, 216, 208/251 H, 309

[56] References Cited UNITED STATES PATENTS 3,155,608 11/1964 Hopper eta1 208/89 3,179,586 4/1965 Honerkamp 208/89 3,362,901 1/1968 Szepe et a1208/ 89 3,732,155 5/1973 Cecil et a1 208/210 3,781,197 12/1973 Bryson etal 208/89 Primary Examiner l-lerbert Levine Hydrogen 1. lea L F- AYSB Or 7 Reduced Y Jan. 14, 1975 ing above the gasoline range and compriseslittle material boiling below the initial boiling point of the residualoil feed. The hydrodesulfurizationdemetallization section comprises aninitial stage involving relatively high hydrogen pressure in thepresence of a catalyst comprising a relatively low proportion ofcatalytically active hydrogenation metals. The process employs a finalhydrodesulfurization stage in series having a relatively lower hydrogenpressure and a catalyst comprising a relatively higher proportion ofhydrogenation metals. The stream entering the final hydrodesulfurizationstage contains an amount up to 10, 20 or even 25 weight percent of theasphaltene content of thecharge to the first stage while the effluentfrom the final stage is essentially free of asphaltenes. The metalscontent of the final stage effluent is so low that said effluent can becharged without blending with a distillate oil to a fluidized zeoliteriser cracking unit (FCC) to produce gasoline and fuel oil. The zeolitecatalyst make-up requirement due to metals accumulation on the zeolitecatalyst is no greater than zeolite make-up requirement when adistillate gas oil comprises the entire feed to the reactor. The sulfurcontent of the final stage effluent is so low that the sulfur dioxidecontent in the zeolite regenerator flue gas is able to meet commercialrequirements and so that the fuel oil range product of the FCC operationis sufficiently low that the FCC fuel oil product also meets commercialfuel oil sulfur specifications without requiring furtherhydrodesulfurization, whereby all hy-- drodesulfurization can precedethe FCC step and no hydrodesulfurization is required after the FCC step.Of course, further desulfurization can follow the FCC step, if such isdesired for a specialized requirement.

9 Claims, 13 Drawing Figures 1 Gus 01123 (Optional Acid Gus Recycle GasH 8 Treatment 30 Light Ratio of Weight Percent Demetallization to Thatat l,400psi Hydrogen Partial Pressure Average Reactor Temperature SHEET10F 9 FIGURE l EFFECT OF HYDROGEN PRESSURE 0N DEMETALLIZATION WITHUNAGED CATALYST 400 600 800 I000 I200 I400 I600 I800 2000 2200 2300(zaKgl (42Kg/ (ssKq/ (roKg/ (a4Kg/ (98Kg/ (nzKg/ (I26Kg/ (l40Kg/(I54Kq/(lslKgl an?) cm t cm cm crri t m5 m3 cm t cm t cm t cm t HydrogenPartial Pressure: psi

(I) 3 .Q (335C) 60 Catalyst Age, Months First Stage PATENTEU JAN 1 41975SHEET 2 OF 9 FIGURE 2 m 0 9 K \J 6 m u m i m m K m w m. 9 K 3 Q 5 i 6 m,3 c. U m O s w s D. m 3 O P 5 9 l m w I e e r r. r a P u F S I 2 5 0 e Hh r I m P P o 2 H H r O P H 7 6 5 4 3 2 Space Time, volume catalyst/vol.

oil/hr.

FIGURE 3 L0 L5 volume cuiulyst/vol.

0.5 Space Time,

Oil/ hr.

p M34159 Jun 4:975

%Demetollizotion /%Desulfurizotion Sam 3 or 9 FIGURE 4 EFFECT OF AGING0N DEMETALLIZATION RELATIVE TO DESULFURIZATION AT SEVERAL HYDROGENPRESSURES I 0 (0.00035 (000070 (0000105 (0.00M (0.00l65 (0002i (000245(0.0028 (000315 (09035 (000385030042 PATENI JAN 4 I915 Average ReactorTemperature sumu'nr 9 FIGURE 6 (e6.6c)l20- 3 (55.5c)lOO 0 III (44.4%) 80O .D (335C) 60 2:- A 0.3% Sulfur, 6Mos. Cycle (222C), 40 B 0.5% Sulfur,IIMos. Cycle C 0.3% Sulfur, IIMos. Cycle (11.1%) 20 O l 1 l I CatalystAge, Days Second Stage Hydrogen i I62 v g Naphgm i Gas oqgl (Optional lI 5 [26 Flgel Acid Gas i Recycle Gas H 8 Tremmem 30 Ugh H-c' TemperatureIncrease Above Base Required For 0.12 Weight PATENTED 3,860,510

' sum 5 or 9 FIGURE 7 Product Sulfur Y 0.4 LHSY\A)4 iexunethol Additionl 0.5OLHSV Percent 0.55 LHSV HI.2C)

IO 5.6 C)

0 IO 7O H0 I30 I50 Catalyst Age (Days) Third Stage PATENT [l] m 1 4197sSHEEI 8 OF 9 FIGURE 9 REACTOR. EFFLUENT CYCLONE VESSEL l'or FLUE GASSTRIPPER 94 STRIPPING STEAM N m m R D O .E E T EN m M m I T D E M R R AER E E P E R T P F E 8 UN R S m w m w /k 0 w L E R m A R E N E G E R 8 7E m NM m mA M m S P R D COMBUSTION AlR AIIR HEATER PATENIED JAN t 4:915

Sulfur Content in 650F+ (343C) Wt.

sum 70F 9 FIGURE IO ow etols toly (Stag I) Low Me tglg w eos otoys tag ih Met ls atcly (Stag Catalyst Requirements For 6 Month Cycle Life ThirdStage Temperature Increase Above Bose Required For O.|2W?.% SulfurProduc1-F PATENTEUJANMBYB 3,860,510

SHEET 9 OF 9 FIGURE I3 -ow Metals Catalyst 2o (Il.2C) 0/ IO 5.6C)

l 2 3 4 5 6 7 8 9 I0 I! I2 Catalyst Aqe- Days COMBINATION RESIDUE IHYDRODESULFURIZATION AND ZEOLITE RISER CRACKING PROCESS This inventionis based upon the hydrodesulfurization of asphaltene-containing residualpetroleum oils having relatively high sulfur and metal contents. Theresidual oils boil above the gasoline range and can have a boiling pointof 375F.+ (l9lC.+), 400F.+ 204c.+), 650F.+ (343C.+) or even '1,050F.+(565C.+).

The present invention is based upon a multiple stagehydrodesulfurization process wherein the effluent from the finalhydrodesulfurization stage is essentially free of asphaltenes asdetermined by pentane extraction and contains less than about 1,generally, or preferably less than about 0.6 ppm of nickel equivalent(nickel equivalent is equal to the ppm by'weight-of nickel plus 1/5 theppm by weight of vanadium which is present). The metals content from theeffluent of the final hydrodesulfurization stage is so low that thetotal final stage effluent without dilution can be employed as theentire stream to a fluid catalytic cracking (FCC) process employing azeolite catalyst in a riser wherein the catalyst and hydrocarbon flow atabout the same velocity without catalyst build-up due to catalystslippage within the riser and without an increase in catalyst to oilratio in the riser. In the FCC process the buildup of nickel andvanadium on the zeolite catalyst is so low when charging undilutedhydrodesulfurization effluent that the zeolite catalyst make-up rate isno more than about 0.2 pounds of zeolite catalyst per barrel of feed(571 g/m) to the FCC riser. This zeolite catalyst make-up rate level isno higher than the normally required zeolite catalyst make-up rate in anFCC riser operation employing a distillate gas oil as the entire feedstream, Of

course, the total hydrodesulfurization effluent can be blended withother streams prior to FCC.

If desired, the present invention can be employed for desulfurizaton ofa full crude oil in the same unit or in separate units. For example, a650F.+ (343C.+) metals containing residual oil can be hydrodesulfurizedin a first unit according to the present invention while the lighterdistillate or a portion thereof can be hydrodesulfurized separatelywithout the problems of metals contamination and high catalystdeactivation. Thereupon, the desulfurized distillate or a portionthereof and the desulfurized residuum can be reblended to provide atotal desulfurized crude for use as a fuel oil or to provide a blendedresidual and distillate oil low in sulfur and boiling above the gasolinerange for feeding to an FCC unit. If a full crude is charged to a singleunit, the gasoline in the effluent is removed by distillation andutilized without cracking.

It is a characteristic of the present operation that thehydrodesulfurization process performs very little hydrocracking of feedoil boiling above the gasoline range, i.e., above about 375F. (191C.) or400F. (204C) to gasoline or lighter materials, i.e., to materi alsboiling below 375F. (191C) or 400F. (204C) This is an important featureof the present process since cracking of feed oil in thehydrodesulfurization operation involves the consumption of hydrogenwhich is wasteful, whereas, if cracking is deferred until the streamreaches the FCC 'unit, gasoline is produced without consumption ofhydrogen and without addition of extraneous hydrogen to the FCC unit.Furthermore,

gasoline produced in the FCC unit without added hydrogen has a higheroctane value than gasoline produced by cracking in the presence of addedhydrogen. Therefore, the function I of the hydrodesulfurization unit isconfined to the removal of sulfur, metals and asphaltenes rather thanthe production of gasoline and the function of the FCC unit is confinedpredominantly to the production of gasoline and also to low-sulfur fueloil with a greater gasoline selectivity based on feed than ifadistillate gas oil feed only were charged to FCC, although the zeolitecatalyst to feed ratio requirement in the FCC riser is not increased toobtain this greater gasoline selectivity in spite of the fact that theentire bottoms portion is being processed in the FCC riser.

While hydrogen is charged to the hydrodesulfurization process,'nohydrogen is charged to the FCC process. The hydrodesulfurization processis essentially free of hydrocracking of feed components boiling abovethe gasoline range feed to material boiling within or below the gasolinerange feed. In the hydrodesulfurization process not more than 20percent, generally, of feed components boiling above the gasoline range,or preferably, not more than 10 percent, and most preferably, not morethan 2 to 5 percent of feed compo-- nents to the hydrodesulfurizationprocess boiling above the gasoline range are converted to gasoline rangeor lighter materials. The hydrodesulfurization process is so free ofhydrocracking to ligher materials that when charging atmospheric towerbottoms, i.e., 650F.+ (343C.+) residue, not more than 25 to 35 percentof this feed will be converted to material boiling below 650F.(343C.).and preferably not more than 20 or 30 percent of this feed willbe converted to material boiling below 650F. (343C). It is thereforeseen that the hydrodesulfurization process is capable ofhydrodesulfurization to produce an effluent wherein or percent by volumeof the feed is recovered having a boiling point at least as high as theinitial boiling point of the hydrodesulfurization feed oil.

In accordance with the present invention, it is shown that in thehydrodesulfurization process at start-of-run with a fresh catalyst, theweight percentage of demetallization increases generally uniformly withincreases in hydrogen partial pressure. Since most of the metal contentof the residual oil is generally present in the asity. Thehydrodesulfurization catalyst comprises at least one Group VIII metaland at least one Group Vl metal on an alumina support containing lessthan 1 weight percent silica. Preferably, the support contains less than0.5 weight percent silica, and most preferably, the support contains aslow as 0.1 weight percent silica. 1

The support can be essentially alumina. It is important that the supportbe sufficiently free of silica so that the catalyst is essentially.devoid of ability to hydrocrack the feed below its initial boilingpoint.

The present invention is based upon the surprising discovery that inhydrodesulfurization the increase in weight percent demetallization in aresidue oil feed with increases in hydrogen partial pressure is atransitory phenomenon only. In accordance with this invention, theunexpected discovery is disclosed that as the catalyst ages the reversesituation rapidly occurs. That is, at the higher hydrogen partialpressures, whereat at the beginning of the run the weight percentage ofdemetallization is the highest, catalyst aging tends to reduce this highratio so that the longer the catalyst ages at a high hydrogen partialpressure the greater the fall off in weight ratio of demetallization todesulfurization. Furthermore, the higher the initial hydrogen partialpressure the more rapid is the fall offin weight ratio ofdemetallization to desulfurization during catalyst agmg.

In contrast, relatively low hydrogen partial pressures, which at startof run conditions produce a reduced weight percentage ofdemetallization, exhibit an in crease in weight ratio of demetallizationto desulfurization in the feed upon catalyst aging. Furthermore, withinthe hydrogen pressure limits of this invention, the lower the hydrogenpartial pressure the more rapid is the increase in weight ratio ofdemetallization to desulfurization upon catalyst aging. In accordancewith this invention, it is important that for optimum demetallization inthe relatively low pressure stages wherein operations preferential todemetallization are desired, that the hydrogen partial pressure not bepermitted to be too low because if the initial rate of demetallizationis too low the increase in demetallization selectivity upon catalystaging is unable to effectively overcome the initial disadvantage withinan acceptably short catalyst aging period. Furthermore, the hydrogenpartial pressure-should not be so low in a hydrodesulfurization stage ofthis invention that excessive and continual coke build-up on thecatalyst is permitted to occur which would lead to an excessively shortcyycle life in the catalyst. The hydrogen partial pressure can be sufficiently low to permit appreciable catalyst coke formation whereby whenequilibrium is achieved the level of coke on the catalyst stabilizes sothat catalyst coke is removed by hydrogenation and leaves the catalystsurface at about the same rate that new coke forms on the catalystsurface.

The present multiple stage hydrodesulfurization process requires thatthe initial stage have a hydrogen partial pressure which is higher thanthe hydrogen partial pressure of the final stage. This is in directcontrast to US. Pat. No. 3,155,608 which is a prior arthydrodesulfurization patent employing multiple stages, which disposeshydrogen recycle and fresh hydrogen streams to produce a higher hydrogenpressure in the final stage than in the initial stage. The pressure dropof this invention can be accomplished by interstage flashing,restrictive pressure drop lines and by regard to points of recycle ofpressurized purified hydrogen or of introduction of fresh hydrogen.Since the hydrogen partial pressure is lower in the final stage andsince excessively low hydrogen partial pressures are conducive tocontinual coke build-up on the catalyst, it is not only necesssary thatthe hydrogen partial pressure in the final stage not be so low that acontinual build-up of coke is permitted but also that the catalyst inthe final stage have a different composition to impart a higherhydrogenation activity as compared to the catalyst in the first stage.Since the catalyst in the first stage is relatively protected againstexcessive coke formation and coke build-up with aging due to elevatedhydrogen partial pressure and since its desulfurization rate is alsoassisted by relatively high hydrogen partial pressure, the first stagecatalyst requires a lower Group VI and Group VIII metal content thanthecontent ofGroup VI and Group VIII metal on the catalyst in the finalstage of the hydrodesulfurization process to balance the aging cyclesbetween the stages and to avoid needlessly excessive active metalsdeposit on the first stage catalyst, which is economically wasteful.Furthermore, because of the low hydrogen pressure in .the final stageand because of its enhanced activity due tQincreased metals content andtherefore increased catalytic sites, the activity of the final stagecatalyst must beprotected in accordance with this invention againstexcessive aging caused by coke build-up by continuous or periodicinjection of a sulfur-containing material such as hydrogen sulfide orhydrogen sulfide-producing hydrocarbon not present in the final stagefeed stream to serve as a catalyst sulfiding agent in the final stage toreplace loss of sulfur from the catalyst and to maintain highhydrogenation activity in the catalyst in the presence of relatively lowhydrogen partial pressure. The particular reason that an extraneouscatalyst sulfiding agent is required in the final stage is that the feedto the final stage has too low a sulfur level and the sulfur in the feedis so refractory that insufficient hydrogen sulfide is produced tomaintain the catalyst at its start-ofrun or presulfided sulfur level. Incontrast, in the first stage the feed is so rich in non-refractorysulfur that the hydrogen-sulfide produced in the first stage not onlymaintains the catalyst at its presulfided fully sulfided level, butbeing a reaction product it even inhibitsthe desulfurization rate in thefirst stage if it is not removed by flashing, as explained below.

In general, the maximum hydrogen partial pressure to be employed in thefirst catalyst stage should not exmed-2,300 to 2,500 psi (161.0 to 175.0Kg/cm and preferably should not exceed 1,900 to 2,000 psi (133.0 to140.0 Kg.cm If higher hydrogen partial pressures are employed in thefirst stage an economic waste will result because as the catalyst agesits initial'advantage in demetallization activity is lost more rapidlyat high hydrogen partial pressures than at lower hydrogen partialpressures so that the highest hydrogen partial pressure to be employedin the first hydrodesulfurization stage can be correlated with thelength of the cycle so that maximum total metals removal can be achievedin the first stage considering the entire length of the catalyst cycle.In accordance with the present invention, and in order to achievecommercial utility, the catalyst cycle. should be at least 5 andpreferably at least 8 and more preferably at least 10 or 12 barrels offeed per pound of catalyst (at least 0.00175 and preferably .at

least 0.00280 and more preferably at least 0.00350 or 0.00420 m /g). Thecatalyst system is balanced so that the high and low pressurehydrodesulfurization stages are capable of about the same cycle lifebefore requiring catalyst regeneration or discard. The quantity andcomposition of catalyst employed in each stage is es-.

tablished to provide as long a cycle life as possible with a minimumtotal quantity of catalyst per barrel of feed, considering the catalystin each stage. Each stage of the hydrodesulfurization process canprovide a cycle life with the available catalyst of at least 4, 5 or 6months or even at least 11 or 12 months.

The hydrogen pressure in the final stage must be balanced so that on theone hand it is low enough that with increasing catalyst age it tends tomaintain or, preferably, to increase the ratio of demetallization todesulfurization which is achieved in the final stage as compared to thefirst stage and so that it provides an effluent which is essentiallyfree of asphaltenes. At the same time the hydrogen partial pressure inthe final stage must be sufficiently high so that there is not anexcessive and continual build-up of coke on the catalyst during the run.In the final stage, because of the relatively low hydrogen partialpressure the asphaltene particles tend to remain at a catalyst site fora relatively long period of time before achieving metal or sulfurremoval and accepting-hydrogen in their place, whereupon the asphalteneparticle leaves the catalyst site and frees the site for acceptance ofanother asphaltene particle to repeat the procedure. Movement ofasphaltene particles to and from catalyst sites occur more rapidly atthehigher hydrogen pressure of the initial hydrodesulfurization reactor andproceeds more slowly at the lower pressure of the finalhydrodesulfurization reactor. The hydrogen partial pressure in the finalhydrodesulfurization reactor should be high enough to at least achievean equilibrium so that after an initial period of operation the build-upof asphaltene particles upon the catalyst surface stabilizes wherebyhydrogenation accompanied by sulfur and metal removal from theasphaltene particle occurs at about the same rate as acceptance of afresh asphaltene particle at the catalyst site. In the finalhydrodesulfurization reactor as asphaltene particle might have to movefrom one catalyst site to another before it is able to accept hydrogenand become demetallized or desulfurized or the reaction may occur at asingle site whereby the asphaltene particle becomes demetallized ordesulfurized and accepts hydrogen at only one catalyst site and becomesconverted to either a resin, an aromatic or a saturate and leaves thecatalyst making the site on the catalyst available for a freshasphaltene molecule. However, because of the requirement for a slowreaction rate in the final stage, an increased number of catalyst sitesare required, and to provide this the weight percentage of active metalsin the final stage catalyst is greater than in the initial stagecatalyst.

The lowest pressure as well as the optimum pressure for theaforementioned functions in the final catalyst stage of this inventionis at least 1,300 or 1,350 psi (91.0 or 94.5 Kg/cm hydrogen partialpressure and preferably 1,400 up to 1,600 or even 1,700, 1,800 or 1,900psi (98.0 up to 112.0 or even 119.0, 126.0 or 133.0 Kg/cm hydrogenpartial pressure. At these pressures, upon catalyst aging anadvantageous balance is reached in ratio of weight percentdemetallization to weight percent desulfurization coupled with astabilization of asphaltene level on the catalyst surface so that theasphaltene level on the catalyst reaches a plateau at which it isremoved and replaced at about the same rate. When this occurs, theeffluent from the final stage is essentially free of asphaltenes.

The hydrogen pressures in the initial and final stages can beestablished in a number of ways. For example, by the hydrogen compressorpressure setting, the amount of diluents in the hydrogen stream and bythe amount and locale of recycle hydrogen injection into the system orby the amount and location of fresh hydrogen injection into the system.The hydrogen pres-' each ofthe stages is about the same. Catalystdeactivation occurs when the average temperature in any stage must beraised from a minimum of about 650 or 690F. (343 or 365C.) to a maximumof from about 790 or 800F. (421 or 427C.) or even 850F. (454C) in orderto stabilize at a desired constant level the sulfur content in theeffluent from a reactor. The tempera tures are continually orintermittently raised in each reactor during a catalyst cycle tomaintain the desired constant sulfur level in the effluent. For'example,the temperatures will be adjusted upwardly continually in the reactorsso that if a residual feed containing about 4 weight percent sulfur ischarged to a three reactor system of this invention, with the reactorsin series, the effluent from the first reactor will contain about 1weight percent sulfur, the effluent from the second reactor will containabout 0.2 toabout 0.5 weight percent sulfur and the effluent from thethird reactor will con tain about 0.05 to 0.1 weight percent sulfur. Inaddition, the effluent from the third reactor will contain less than 1and preferablyvless than 0.6 weight percent nickel equivalent (which isthe ppm of nickel plus 1/5 of the ppm of vanadium) when the feed to thefirst reactor contains 60 ppm of nickel plus vanadium, or more. Also,the effluent from the third reactor will be essentially free ofasphaltenes, as measured by conventional means, i.e., no normal pentaneinsolubles will be detected in a normal pentane extraction of theeffluent.

The total catalyst quantity required to achieve the hydrodesulfurizationresults of this invention will be sharply minimized by employing ahigher Group V1 and Group VIII metals weight level catalyst in thefinalthis sulfur is so refractory, there is a dearth of sulfur in theatmosphere of the final stage resulting in a loss of sulfur from thepresulfided final stage catalyst, tending I to cause the final stagecatalyst to deactivate more rapidly than the catalyst in any earlierstagev This loss of sulfur can result in a runaway buildup ofasphaltenes upon the surface of the catalyst. in the final stage due toloss of hydrogenation activity. In order to stabilize and equalizeasphaltene adsorption and desorption at the surface of the catalyst inthe final stage, it is necessary to provide hydrogen sulfide orothersulfiding agent not present in the oil feed to the catalyst of the finalstage so that the cycle life in the final stage is as long as the cyclelife in the earlier stages, i.e., each reactor reaches its temperaturelimitation of about '800F. (427C.) at about the same time. We have foundthat the addition of a sulfiding agent to the final stage can result ina nearly flat aging curve in the final stage. The sulfur addition to thefinal stage can be received directly by hydrogen sulfide injection, byinjection of a hydrogen sulfide producing organic material not presentin the feed oil or can be produced from the feed stream in an earlierand higher pressure hydrodesulfurization stage and transmitted to thefinal low pressure stage by passing the effluent from an earlier higherhydrogen pressure hydrodesulfurization stage containing hydrogen sulfideundiluted by fresh or make-up hydrogen to the final hydrodesulfurizationstage without any flashing or hydrogen sulfide absorption step prior tothe final hydrodesulfurization stage.

The catalyst in all phases comprises at least one Group VI and at leastone Group VIII metal in sulfided condition, such asnickel-cobalt-molybdenum on alumina. Many metals combinations can beemployed, such as a cobaltmolybdenum, nickel-tungsten andnickel-molybdenum. A noncracking alumina support must be employed, suchas an alumina containing less than 1 weight percent silica, preferablyless than 0.5 weight percent silica and most preferably no more than 0.1weight percent silica. The metals content on the catalyst is higher .inthe final stage than in the initial stage. Whatever, metals content isemployed, the'weight percent of active Group VI-G'roup VIIIhydrogenation metals in the final stage is higher than in the initialstage.

The present invention is directed towards the hydrodesulfurization of aresidual oil containing substantially the entire'asphaltene fraction ofthe crude from which it is derived and which therefore contains 95 to 99weight percent or more of the nickel and vanadium content ofthe fullcrude. The nickel, vanadium and sulfur content of the liquid charge canvary over a wide range. For example, nickel and vanadium can comprise0.0005 to 0.05 weight percent(5 to 500 parts per million) or more ofthefeed oil while sulfur can comprise about 2 to 6 weight percent or moreof-the charge oil.

In the hydrodesulfurization process of this invention it is the partialpressure of hydrogen rather than total reactor pressure which determineshydrodesu1- furization and demetallization activity. Therefore, thehydrogen stream should be possible.

The gas circulation rate can be between about 2,000

and 20,000 standard cubic feet per barrel (between about 36.0 and 360.0SCM/100L), generally, or preferably about 3,000 to 10,000 standard cubicfeet per bar-' rel of gas(54.0 to 180.0 SCM/lOOL), and preferablycontains 80 percent or more of hydrogen. The mol ration of hydrogen tooil can be between 8:1 and 80:1. Reactor temperatures can range betweenabout 650 and 900F. (343 and 482C), generally, and between about 680 and800F. (360 and 427C), preferably. The temperature should be low enoughso that not more than about 10, or percent of a 650F. (343C.+) residualoil charge will be cracked to furnace oil or lighter. At reactor outlettemperatures of 800 to 850F. (427 to 454C.) the steel of the reactorwalls rapidly loses strength and unless reactor wall thicknesses of 7 to10 inches (17.78 to 25.40 cm) or more are utilized, a reactor outlettemperature of about 800 to 850F. (427 to 454C.) constitutes ametallurgical limitation. The liquid hourly space velocity in eachreactor of this invention based on hydrocarbon oil feed to the firststage can be between about 0.2 and 10, generally, between about 0.3 and3, preferably, or between about 0.5 and 15, most preferably.

The catalyst employed in the process, as stated above, comprisessulfided Group VI and Group VIII metals on a support, such as sulfided,nickel-cobaltmolybdenum or cobalt-molybdenum on alumina. Hy-

as free of other gases as drodesulfurization catalyst compositionssuitable for use in the present invention are described in US. Pat.

No. 2,880,171 and also in US. Pat. No. 3,383,301.

However, an advantageous feature ofthe catalyst particles of the presentinvention is that the smallest diameter of these particles is broadlybetween about H20 and 1/40 or l/50 inch (0.127 and 0.0635 or 0.051 cm),preferentially between 1/25 and 1/36 inch (0.102 and 0.071 cm), and mostpreferably between about 1/29 and l/34 inch (0.081 and 0.075 cm).Particle sizes below the range of this invention would induce a pressuredrop which is too great to make them practical. The catalyst can beprepared so that nearly all or at least about 92 or 96 percent of theparticles are within this size range. The catalyst can be in anysuitable configuration in which the smallest particle diameter is withinthis size range, such as roughly cubical, needleshaped or roundgranules, spheres, cylindrically-shaped extrudates, etc. By smallestparticle diameter is meant the smallest surface to surface dimensionthrough the center or axis of the catalyst particle, regardless of theshape of the particle. The cylindrical extrudate form having a lengthbetween about 1/10 and 4 inch (0.254 and 0.635 cm) is highly suitable.

It is important in this inventionthat the catalyst is essentially freeof dehydrogenation activity to prevent formation of severely hydrogendeficient coke on the catalyst. It is to be emphasized that thehydrocarbon build-up in the final stage catalyst is not a severelyhydrogen-deprived material initially but is essentially an asphaltene orcoke precursor material as received in the feed stream containingsomewhat higher than the feed hydrogen to carbon ratio. Because thecatalyst has not rendered the feed asphaltene hydrogen deficient, theasphaltene is capable of undergoing desulfurization and demetallizationaccompanied by a reception of hydrogen to convert the feed asphaltene toa more hydrogenrich molecule such as a resin, an aromatic, or asaturate, which can then leave the catalyst site by dissolving into themain flow stream in the final reactor, thereby stabilizing theasphaltene content on the catalyst. An indication that the catalystsupport of the present invention is not a hydrocracking or coke. forming(i.e., a hydrogen depriving) catalyst is illustrated by the fact thatincreasing hydrogen pressures with the catalyst does not result in anydetectable or significant increased hydrogen consumption. Furthermore,after brief conditioning of the catalyst under the same conditions oftemperature, pressure and residence time, the amount of hydrocrackingexperienced with the catalyst of the present invention is about the sameas that experienced with inert solid particles.

The various stages in series of the hydrodesulfurization process of thepresent invention are balanced with respect to hydrogen partialpressure, relative catalyst volume and catalyst activity in order toencourage balancing of relative metals removal in each of the stages.For example, in a three-stage operation, the I quantity of asphaltenesand metals will be greatest in the first stage, intermediate in thesecond and smallest in the third stage. To compensate for this, thepercent reduction of asphaltenes and metals in the first stage will bethe lowest, will be intermediate in .the second stage and will be thehighest in the third stage. As an example, consider a residual feed tothe hydrodesulfurization process of this invention containing about 10weight percent asphaltenes, about 5 percent will be thermally cracked orrendered into smaller structures by the enhanced solubility in aromaticsat the high hydrogen pressure of the first stage. The remaining 5percent will be more refractory to hydrocracking than most of those inthe feed. Since the first stage possesses the highest hydrogen partialpressure, whatever asphaltenes are refractory to hydrocracking in thefirst stage will not be thermally cracked at as great a rate in thesubsequent stages since the subsequent stages are at a lower pressure.If they were not amenable to cracking at the higher pressure of thefirst stage they will be less amenable to hydrocracking at the lowerpressures of the subsequent stages. Of the percent of the asphaltenesfed to the first stage which is refractory to hydrocracking, about 2percent will be adsorbed on the first stage catalyst whereat it will bedemetallized and/or desulfurized. This amounts to a 40 percent reductionin asphaltenes in the. first stage by adsorption on the catalyst. Theremaining 3-percent of asphaltenes in the feed enter the secondhydrodesulfurization stage, and in the second stage, of this 3 percent,2 percent will be ad sorbed on the second stage catalyst where it willbe de sulfurized and/or demetallized, amounting to a 67 percentreduction of asphaltenes by adsorption on the catalyst in the secondstage. This leaves 1 percent of the total asphaltenes in the feed forentry into the third catalytic stage. In the third catalytic stageessentially the entire l percent is adsorbed on the catalyst and isdemetallized and/or desulfurized for subsequent dissolution into thehydrodesulfurization product stream as a resin, aromatic or saturatemolecule, so that the effluent stream of the third stage is essentiallyfree of asphaltenes. Assuming that reduction in asphaltenes in the aboveexample generally corresponds to absorption the second stage toessentially 100 percent reduction of metals in the third stage. However,while the percent reduction in metals is increasing in each stage, theabsolute quantity of metals removed is progressively diminished in thestages so that there tends to be a balance of absolute quantity ofmetals removal in the various reactors of the system. However, it isemphasized that there is a progressively smaller absolute amount ofmetals removal in each subsequent stage. This balance is importantbecause while asphaltene particles reach an equilibrium so that theyaccumulate and are removed at about the same rate on the catalystsurface, the metals that build-up can not be removed by ordinary-meansduring the process and they therefore contribute toward irreversiblelimitation of the catalyst cycle in each reactor. 1

Data are shown below which illustrate not only the optimum and theminimum hydrogen pressure to be employed in the finalhydrodesulfurization stage (the optimum is about 1,400 psi [98.0 Kg/cm lhydrogen partial pressure) but also the optimum and maximum hydrogenpartial pressure to be employed in the initial hydrodesulfurizationstage. These data show that at very high pressures (2,300 psi [l6l.0Kg/cm hydrogen partial pressure) the asphaltene content of the catalystwas reduced but the sulfur content of the remaining asphaltenes changedvery little. This indicates that the higher pressure performed acatalytic effect in hydrocracking the asphaltenes to lighter moleculeswithout appreciable removal of metal or sulfur which require relativelyextended adsorption time at a catalyst site for their occurrence.Evidently at the higherhydrogen pressure of 2,300 psi [161.0 Kglcm leven the briefest contact with a catalyst site resulted in very rapidreaction thereupon the molecule became hydrogenated to a less refractoryasphaltene or a nonasphalteneor became hydrocracked to smaller fragmentsbefore enough time elapsed at the catalyst site to permit removal ofsulfur or metals. The same tests show that at the lower hydrogen partialpressure of 1,950 psi (136.5 Kg/cm there was essentially no change inthe asphaltene content in the feed oil although the sulfur content inthe asphaltenes was diminished sharply. These data indicate that at thelower pressure the asphaltenes adsorbed on the catalyst site werepermitted sufficient residence time for removal of metals and sulfuralthough the pressure was not sufficiently high to accomplish muchhydrogenation to less refractory nonasphaltenic material and/orhydrocracking. These, tests indicate that at a pressure as high as 2.300psi (161.0 Kg/cm desulfurization of asphaltenes does not occur to assignificant an extent as at low hydrogen partial pressures; These testswere taken with an aged catalyst in the first reactor.

In FCC operations the sulfur concentration is highest in the higherboiling product fractions of the FCC product. It is an importantadvantage of this invention that the sulfur content of thehydrodesulfurization effluent is so low that even the fuel oil range(400 to 650F. [204 to 343C]) product of FCC has a sulfur content below0.25 weight percent, preferably below 0.20 weight percent, which meetscommercial specifications for home heating oil in the United States, sothat further desulfurization of the fuel oil is not required. This isunusual since usually furnace oil range product from FCC operations mustbe desulfurized to' meet home heating oil sulfur commercialspecification. Therefore, the hydrodesulfurization-FCC combinationprocess of this invention accomplishes all required desulfurizationrequirements in advance of the FCC step with no desulfurizationoperation required after the FCC operation. A further and importantadvantage of this fact is that. because the sulfur is'removed from thefeed in advance of FCC, rather than following FCC, the sulfur dioxide inthe FCC regenerator off-gas which comes from sulfur-containing coke onthe zeolite catalyst, is minimized to a level meeting commercialrequirements without scrubbing of sulfur dioxide from the regeneratorflue gas. It is extremely difficult to scrub sulfur dioxide in a fluegas stream and high sulfur dioxide levels in FCC regenerators arerapidly becomming an unacceptable source of air pollution. In accordancewith this invention this difficulty is obviated.

The characteristics of the hydrodesulfurization process discussed aboveare illustrated in the data shown in the attached figures. FIG. 1 showsthe effect of hydrogen partial pressure upon the ratio of weight percentdemetallization, using demetallization at 1,400 psi (98.0 Kg/cm hydrogenpartial pressure as a base, of

a residual oil employing a fresh (unaged) relatively low active metalslevel hydrogenation catalyst of the first hydrodesulfurization reactionstage of this invention. As shown in FIG. 1, data taken with an unagedlo'w metals catalyst show that an increase of hydrogen partial pressureresults in an increase in demetallization. Since most of the metalspresent in the feed are present in the asphaltene fraction of the feed,an increase in demetallization represents a decrease in asphaltenecontent of the stream passing through the reactor. FIG. 1 tends toindicate that a residual oil hydrodesulfurization process'wherei-n it isdesired to produce a product having a very low metals level, such as ahydrodesulfurization process to convert a high metalscontaining residualoil to a good quality FCC feed stream which will not unduly deactivatethe FCC zeolite catalyst by excessive metals deposit thereon, requiresas high a hydrogen partial pressure as possible. However, FIGS. 2 and. 3illustrate the discovery of the present invention indicating that thedata of FIG. 1 are misleading and that as the catalyst ages if it isdesired to convert a residual oil via hydrodesulfurization in aprolonged catalyst aging cycle to a product having a relatively lowsulfur and metals content, while employing a relatively small quantityof hydrodesulfurization catalyst, it is not desirable to operate thetotal hydrodesulfurization process uniformly at a high pressure butrather it is more advantageous to operate the hydrodesulfurizationsystem employing both a high pressure phase and a low pressure phase.The pressures in the stages should be selected to provide an economicoptimum quantity of.catalyst in the stages based on the length of thecatalyst cycle desired.

FIGS. 2 and 3 illustrate residual oil hydrodesulfurization data with arelatively low hydrogenation metals catalyst of the firsthydrodesulfurization stage of this invention under high pressureconditions including a run at 2,300 psi (161.0 Kg/cm hydrogen partialpressure and a lower pressure run at 1,950 psi (136.5Kg/cm hydrogenpartial pressure. FIG. 2 shows that at the higher hydrogen partialpressure of 2,300 psi (161.0 Kg/cm asphaltene content diminishes at arelatively rapid rate whereas at 1,950 psi (1365 Kg/cm hydrogen partialpressure there is substantially no change in asphaltene content. Theruns of FIGS. 2 and 3 were made with a catalyst that had been aged andnot with the fresh catalyst. FIG. 3 represents the same tests as shownin FIG. 2 but illustrate what appears to be an opposite result. The dataof FIG. 3 show that at the higher hydrogen partial pressure of 2,300 psi(161.0 Kg/cm there occurs very little reduction in sulfur content in theasphaltene fraction of the stream while at the lower pressure of 1,950psi (136.5 Kg/cm there is a much-greaterreduction in sulfur content inthe asphaltene fraction.

The dashed line in FIG. 2 indicates that at a much I higher hydrogenpartial pressure of 3,000 psi (210.0

Kg/cm asphaltenes could be completely removed in a single reactor at aspace time of about 1, completely removing the problem of asphaltenesulfur content in the oil in one stage. However, at-such a high pressurethe reactor thickness and operating costs would be excessive andimpractical. It is the purpose of the present invention to employ alower pressure mode of operation to completely remove asphaltenes in aplurality of stages, and more particularly to arrange the stages toutilize a plurality of hydrogen pressures, whereby reactor thickness andcatalyst costs are not excessive. When employing a plurality ofpressures, it'is important to completely remove asphaltenes at as low afirst stage pressure as possible, since the second phase pressure mustbe a step-down from the first and an excessive pressurestep-down'would-be wasteful.

Although the solid line data of FIGS. 2 and 3 appear to becontradictory, they illustrate the underlying discovery of the presentinvention and show the unexpected nature of this discovery. Referring toFIG. 2, at the 2,300 psi 161.0 Kglcm hydrogen partial pressure theasphaltene content diminishes rapidly as compared to the 1,950 psi(136.5 Kg/cm pressure test because at the 2,300 psi (161.0 Kg/cmpressure, it is pressure rather than residence time at a catalyst sitethat appears to be controlling. An asphaltene particle present at acatalyst site at the relatively high hydrogen partial pressure of 2,300psi (161.0 Kg/cm reacts very readily so that at a very short residencetime at the catalyst site the asphaltene particle is able to chemicallyaccept some hydrogen to increase its hydrogen to carbon ratio and eitherbe converted to a less refractory resin and/or become hydrocracked to alower-boiling saturate or aromatic compound. At the 1950 psi (136.5Kg/cm test condition, the pressure is not high enough to accomplish muchhydrocracking and therefore an asphaltene molecule reacting at thecatalyst site at the 1,950 psi 136.5 Kg/cm pressure does not undergohydrocracking but remains an asphaltene. FIG. 3 shows that at the 1,950psi (136.5 Kg/cm hydrogen partial pressure test condition the lack ofextensive hydrocracking permitted the asphaltene molecule to remain atthe catalyst site sufficiently long to become more extensivelydesulfurized, specifically, because it was not first hydrogenated orhydrocracked and thereby enabled to readily leave the catalyst site.Therefore, at the lower pressure the catalytic effect tends to becomecontrolling in preference to the asphaltene adsorption effect caused bythe change in pressure. Therefore, the longer residence time atthe.1,950 psi (136.5 Kg/cm pressure does not diminish the. asphaltenecontent in the stream but it does substantially reduce the sulfur levelin the feed asphaltenes, which feed asphaltenes tend to remain asasphaltenes. On the other hand, as shown in FIG. 3, at the 2,300 psi(161.0 Kglcm pressure, the hydrogen pressure effect tends to becomecontrolling over the catalytic effect, causing the residence time at thecatalyst site to be so brief-the sulfur content of the asphaltenes thatremained in the stream was diminished very little. This shows thatalonger residence time at the catalyst site is required toaccomplishdesulfurization of asphaltenes (desulfurization being a'highly-catalyticeffect) than is required to merely add hydrogen to the asphaltenemolecules and thereby to hydrocrack asphaltene molecules and the longerresidence time is accomplished by reducing hydrogen pressure. In thismanner, the rate of hydrogenolysis of the asphaltenes is no greater thanor is less than the rate of desulfurization, thereby allowing thecontrolling reaction to be a desulfurization of those asphaltenes whichdo not readily react to become smaller compounds.

An important feature of the showing of FIGS. 2 and 3 is that thehydrocracking and/or hydrogenation (i.e., hydrogenolysis) that occurredat the 2,300 psi (161.0 Kg/cm hydrogen partial pressure, while itdiminished asphaltene content in the flowing stream, merely producedproducts containing only a slightly reduced quantity of sulfur andmetals in the asphaltenes. On the other hand, the test made at the 1,950psi (136.5 Kg/cm hydrogen partial pressure, while-it did not reduceasphaltene content in the flowing stream, did succeed in sharplyreducing sulfur (and also metals) content in the asphaltene flowingstream. FIGS. 2 and 3 therefore show that if effective desulfurizationand demetallization is to occur in the asphaltene fraction, it isimportant that the hydrogen partial pressure in the first stage of thehydrodesulfurization process of the present invention need not be toohigh, resulting in lower costs for equipment. The data indicate thatmuch greater sulfur removal from the asphaltenes is accominvention withthe relatively low Group VI-Group VIII metals content catalyst of thisinvention should be less than 2,300 psi (161.0 Kg/cm and preferably lessthan 2,100 or 1,900 psi (147.0 or 133.0 Kglcm hydrogen partial pressure.The hydrogen partial pressure to be employed will generally be dependentupon feed properties.

FIG. 4 illustrates another unexpected discovery related to the effect ofhydrogen partial pressure upon catalyst aging. The data shown in FIG. 4also illustrate a catalyst aging effect opposite to the effect shown inthe data of FIG. 1. FIG. 4 shows the results of pilot plant aging testsconducted in the initial reactor of applicants hydrodesulfurizationprocess with a 50 percent reduced Kuwait crude residual feed employingan alumina-supported hydrodesulfurization catalyst having the relativelylow Group VI-Group V111 metals content of this invention. The data ofFIG. 4 show the effect of aging on the ratio of percent demetallizationto percent desulfurization at various hydrogen partial pressures. FIG. 4shows that at zero catalyst age the higher the hydrogen partial pressurethe higher is the ratio of percent demetallization to percentdesulfurizain FIG. 1, which was made with a fresh catalyst. However, theunexpected showing of FIG. 4 is that with increasing age the exactopposite effect occurs. That is, with increasing catalyst age, highhydrogen partial pressures cause the ratio of percent demetallization topercent desulfurization to become progressively lower. FIG. 4 shows thatalthough the data curve for a 2,300 psi (161.0 Kglcm hydrogen partialpressure test initially exhibits the highest ratio of all the tests, thedecline in selectivity for metals over sulfur removal with increasingage is the steepest at this high pressure. FIG. 4 shows that-althoughthe data for the 1,830 psi 128.1 Kg/cm test initially has a lower ratioof demetallization to desulfurization, at this pressurethere is a lossin demetallization selectivity at a lower rate, so that after an age ofabout 5 barrels of feed per pound of catalyst (0.00175 m /g), this testpressure surpasses the 2,300 psi (161.0 Kg/cm test in demetallization todesulfurization ratio. The test made at 1,660 psi (116.2 Kg/cm hydrogenpartial pressure had a still lower initial demetallization selectivity,but with aging the demetallization activity actually tends to increaseso that after only about a catalyst age of 2 barrels per pound (0.00070m lg) the demetallization to desulfurization ratio for the 1,660 psi(116.2 Kg/cm test is higher than the ratio for the 1,830 psi (128.1Kg/cm test. It is noteworthy that the tests made at the relatively highpressures of 2,300 psi (161.0 Kg/cm and 1,830 psi (128.1 Kg/cm both havenegative slopes indicating a decline in demetallization selectivity withcatalyst aging in an extended aging test. The test made at 1,660 psi(116.2 Kg/cm?) hydrogen partial pressure is the highest pressure testmade which exhibits a positive slope. i.e., which shows an actualincrease in ratio of weight percent demetallization to weight percentdesulfurization with increasing catalyst age. At progressively lowerhydrogen partial pressures between 800 psi (56.0 Kg/cm and 1,660 psi(116.2 Kg/cm the ratio curve becomes increasingly steep with catalystaging. At a pressure generally between 1,700 and 1,800 psi (119.0 and126.0 Kg/cm the selectivity aging curve changes in slope from negativeto positive. It is noted that these values are representative ofaparticular feedstock and catalyst. It also is noted that the tests ofall the curves of FIG. 4 were made at temperatures which werecontinually or intermittently increased so that a 4 weight percentsulfur feed stream was converted to about a 1 weight percent sulfureffluent, except that the effluent sulfur in the 1,200 psi (84.0 Kg/cmtest was 1.12 weight percent and in the 800 psi (56.0 Kg/cm test theeffluent sulfur was 1.5 weight percent due to v the fact that it wasalmost impossible to raise temperaressed the sulfur content in theeffluent was permitted to increase from 1.0 weight percent to 1.9 weightpercent.

Referring again to FIG. 4, the test at 1,400 psi (98.0 Kg/cm shows thehighest ratio of percent demetallization to percent desulfurization ofall the tests made. The test made-at 1,400 psi (98.0 Kg/cm achieves thishigh ratio because of two factors. First, its initial activity at thispressure is not so exceedingly low that it cannot be overcome by apositive aging slope. Secondly, the aging slope is sufficiently steep sothat, combined with the relatively high initial catalyst activity, the1,400 psi (98.0 Kglcm pressure achieves high demetallization rates veryearly in the run. For example, the

demetallization ratio in the 1,400 psi (98.0 Kg/c'm l run exceeds thedemetallization ratio for the 1,830 psi (128.1 Kg/cm run at a catalystage of only 1 barrel 7 made at 800 and 1,200 psi (56.0 and 84.0 Kg/cmwere so low that-in spite of the steepness of the slope of thedemetallization curves upon aging at these two pressures, an excessivelygreat time duration elapsed before an appreciably high demetallizationratio was achieved. According to the data shown in FIG. 4, the finalphase reactor is best operated at a pressure of about 1,400 psi (98.0Kg/cm) of hydrogen and generally between 1,300 psi (91.0 Kglcm and 1,600psi (112.0 Kg/cm or 1,700 psi (119.0 Kg/cm of hydrogen. An optimumpressure range would be about between 1,300-psi (91.0 Kg/cm or 1,350 psi(94.5 Kg/cm l and 1,500 psi 105.0 Kglcm hydrogen'pressure. Best resultsare obtained when the first and final stage hydrogen pressures pass thethreshold values wherein the percent demetallization/percentdesulfurization v. catalyst age is slightly negative in the first stagewhereas this same slope is positive in the final stage.

FIG. 4 showsruns conducted at a sufficiently low pressure that thecontrolling feature in the reactor is the absorption and residence timeof asphaltene at a catalyst site or sites. At these low hydrogenpressures, significant hydr ocracking or hydrogenation activity does notoccur and therefore an asphaltene molecule contacting a catalyst sitetends to reside at the site or to move to another catalyst site for asignificant total catalyst residence time before reaction can occur. Dueto the lengthened on-catalyst residence time at low hydrogen partialpressures, the reaction that occurs is not apt to be hydrocracking orsimple hydrogenation but is more apt-to be removal of metals and sulfuraccompanied by an acceptance of hydrogen to provide a loss of metal andsulfur from the asphaltene molecule. At the low pressures, such as 1,400psi (98.0 Kglcm the residence time required is sufficiently great that asignificant build-up of asphaltene molecule occurs upon the surface ofthe catalyst. The asphaltene content on the catalyst may reach about 20to 40 percent by weight of catalyst, as compared with a coke level onthe catalyst in the first or high pressure hydrodesulfurization stage ofonly about 51 5 weight percent. However, at the low.

pressure stage and with the high level of hydrogenation metals on thelow pressure catalyst, the asphaltenes do not tend to dehydrogenate andform what is known as carbon or coke of very low hydrogen content.Instead, they tend to remain as asphaltenes and to reside at thecatalyst site while they slowly desulfurize and demetallize. Uponreacting by loss of sulfur and/or metal, they then may leave thecatalyst and may be replaced by a fresh asphaltene particle. In themolecules leaving the catalyst, the void left by the removed metal orsulfur is replaced by hydrogen so that the ratio of hydrogen to carbonin the molecule is increased and the treated molecule is no longer anasphaltene. In this manner, a substantial equilibrium level ofasphaltenes is rapidly achieved on the surface of the catalyst. Althoughthe residence time required for reaction is low due to the relativelylow hydrogen partial pressure, the hydrogen pressure is selected inrelation to the Group VI-Group VIII metals level on the catalyst so thatanequilibrium level of asphaltenes on the catalyst is achieved. At theequilibrium level or plateau there is no significant increase ordecrease in asphaltenes content on the surface of the catalyst andasignificantly long aging run can be achieved so that the total catalystage before deactivation, that is, before the catalyst reaches atemperature of 790 or 800F. (421 or 427C), or above, de-

pending. upon reactor metallurgy, to achieve the desired effluent metalsand sulfur level is as great or is balanced in the final reactor ascompared to length of the run in the initial or high pressure reactor.

It is noted that the very high percentage metals removal level is onlyuseful in the final reactor where the total asphaltene and metalsconcentration in the stream is already low and not in the initialreactor where the total asphaltene and metals level is high where veryhigh percentage removal of metals would result in excessively rapidcatalyst aging. Therefore, in the balanced hydrodesulfurization systemof this invention, the life of the catalyst in the initial stage ismetalslimited while the life of the catalyst in the final stage iscoke-limited, with the life cycles being essentially bal- ,anced.

FIG. 4 shows that in a lengthy commercial operation of at least or 12-barrels of feed oil per pound of catalyst (0.00350 or 0.00420 m /g), theonly runs that achieved a weight ratio of demetallization todesulfurization of greater than 1 at both start-of-run and endof-runwere the 1,400, 1,660 and 1,830 psi (98.0, 116.2 and 128.9 Kg/cm runs. Aratio greater than 1 indicates the reactor is primarily an asphalteneremoval reactor since most metals are concentrated in the asphaltenes.Since the third stage is capable of maintaining percent demetallizationto percent desulfurization ratios greater than 1, and can produce anasphaltene-free effluent throughout the cycle of 10 12 barrels per pound(000350 -0.00420 m /g), a considerable savings in catalyst cost isrealized by employing a relatively lower Group VI-Group VIII metalcatalyst in the first or first and second stages since a high proportionof catalyst cost is based on the Group VI- Group VIII metals contentthereon. Depending on the space velocities employed, FIG. 4 showscatalyst life cycles of 4, 5, 6 or even 11 or 12, or more, months ispossible before regeneration or discarding of the catalyst.

FIG. 5 shows a typical aging run in a first stage reactor of thisinvention in terms of catalyst age versus increase in reactiontemperature to reduce a 650F.

(343 "C.+) residue from about 4 weight percent sulfur to about 1 weightpercent sulfur at about 1,830 psi (128.1 Kg/cm partial pressure ofhydrogen with a relatively low hydrogenation metals content catalyst ofthe present invention.

FIG. 6 shows similar aging runs at various space velocities (asreflected by cycle lengths) wherein the effluent from the test of FIG.5, after being flashed to remove hydrogen sulfide and lighthydrocarbons, and after receiving fresh hydrogen to be repressurized toabout nearly the same hydrogen pressure as the hydrogen pressure in thefirst reactor, and employing a similar low hydrogenation metals catalystas employed in the first reactor, is further treated in a second reactorto reduce the sulfur content from about 1 weight percent down to either0.3 or 0.5 weight percent sulfur.

FIG. 7 shows the results of aging runs made in the third and finalhydrodesulfurization reactor of this invention. A comparison of FIG. 7with FIGS. 5 and 6 shows that the aging rate of the third reactor (FIG.7) is much more rapid than the aging rate in the earlier reactors andthe catalyst in the third reactor cannot last the full cycle reached inthe earlier reactors unless special steps are taken in the thirdreactor, as described, which are not required in the first two reactors.The third reactor was operated at 1,700 psi 1 19.0 Kg/cm") hydrogenpartial pressure and contained a catalyst having a higher Group VI-GroupVIII metals content than the catalyst of the first two reactors. It isemphasized that the feed to the final reactor, after having its sulfurcontent reduced to 0.3 0.5 weight percent, has remaining in it the mostrefractory sulfur and also the most refractory metals present in thefeed oil. This remaining sulfur and metals content is probably mostrefractory because, for example, it is the feed sulfur and metalscontent which is the most deeply embedded within the interior of thefeed asphaltene or resin molecules. By the time the stream reaches thefinal stage, most of the sulfur and metals content of thev total streamis present in the remaining asphaltenes. Most of the less refractorysulfur and metals, i.e. the metals closest to the fringe of theasphaltene molecule, are more readily removed and are extracted in thefirst two stages. Because the sulfur and metals content in the streamentering the final stage contains the most refractory metals and sulfur,the asphaltenes in the stream require the longest residence time at acatalyst site. They also require a catalyst which is enhanced inhydrogenation activity as compared to the catalyst used to remove lystsite, just as high hydrogen pressure in an initial .stage tends toinhibit asphaltene residence time at a catalyst site. Furthermore,because the sulfur level in invention and the hydrogen sulfide producedin the second stage is passed'to the third stage and is used as a sourceof sulfur for maintaining the third stage catalyst in a highly sulfidedcondition, as is required for maintaining its activity.

The lack of hydrogen sulfide in the third reactor causes the catalyst tolose sulfur so as to maintain an equilibrium, with respect to hydrogensulfide, between the catalyst, the liquid and the gas phases. Ifthecatalyst is to be maintained in an adequately sulfided state, it isnecessary for the reaction stream to contain a sufficient quantity withhydrogen sulfide by maintaining a hydrogen sulfide atmospherevin thegases in contact with reaction stream. If there 'is insufficienthydrogen sulfide gas in contact with the stream to the reactant liquidsaturated with hydrogen sulfide, the feed' liquid will drain sulfur fromthe catalyst. But if there is sufficient gaseous hydrogen sulfide tosaturate the feed liquid, the liquid will not tend to reduce the sulfurlevel of the catalyst. Therefore, it is important that sufficienthydrogen sulfide is added to the third stage to keep the liquid in thethird stage saturated with hydrogen sulfide and this can only beaccomplished if there is sufficient hydrogen sulfide partial pressureabove the liquid to maintain the active catalytic metals in a fullys'ulfided state.

The test made in FIG. 7 illustrates the importance of external additionof sulfur to the final stage catalyst, whether this sulfur comes fromthe previous stage, is injected as hydrogen sulfide or' is injected asan extraneous organic sulfur-containing compound which is easilyconvertible to hydrogen sulfide. The data illustrated by the triangledata points in FIG. 7 were taken to simulate the final stage of thehydrodesulfurization process of this invention except that no hydrogensulfide from any source was added with the feed. As shown, the agingslope was steep throughout the run. However, the data in FIG. 7illustrated by the square shaped points show a feed also devoid ofhydrogen sulfide from any source until the region A denoted byhexanethiol addition was reached. The aging curve was just as steepuntil reaching region A. At region A, the sulfur containing compoundhexanethiol was added with the feed in order to contribute sulfur forsulfiding of the catalyst. As shown in FIG. 7, when the hexanethiol wasadded the aging rate became stabilized and the curve became relativelyflat, indicating essentially no further catalyst aging during thesulfiding of the catalyst. After the hexanethiol addition wasterminated, at the end of the flat region A, the aging rate againincreased, indi- Of course, the addition of hydrogen sulfide is notharmful from the point of view of reducing the hydrogen partial pressurebecause, as explained above, the final stage of the hydrodesulfurizationprocess of this invention operates most advantageously at low hydrogenpartial pressures. Tests were made in which the substitution of otherhydrogen sulfide precursors, such as butanethiol, thiophene andethanethiol were also found to provide a flat aging rate in the thirdstage.

The dearth of hydrogen sulfide is not noticed early in a test butdepends upon the length of the test and the amount of catalyst present.A lack of hydrogen sulfide in the third reactor atmosphere results ininitial desulfurization of the top of the third stage catalyst bedcoupled with a covering of catalyst sites with hydrogendeficienthydrocarbons, shifting the reaction burden to progressively deeperregions of the bed which are not yet desulfided. It is only when thedesulfurization of the catalyst and covering of the catalyst sites withhydrogen deficient hydrocarbons reaches sufficiently deeply into thecatalyst bed leaving insufficient fully sulfided and non-coated catalystremaining, that the lack of hydrogen sulfide becomes apparent.Therefore, the lack of hydrogen sulfide is not immediately apparent inthe third stage at start-of-run. Also', after a desulfided catalyst isresulfided onstream during a run by extraneous hydrogen sulfideaddition, termination of hydrogen sulfide addition does not show adeleterious effect upon aging rate until the desulfiding and catalystcoating procedure has again progressed sufficiently deeply into the bedthat insufficient fully sulfided and uncoated catalyst remains.

FIG. .8 schematically illustrates a preferred threestagehydrodesulfurization process of this invention. As shown in FIG. 8, areduced crude such as a 650F.+ (343C.+) Kuwait reduced crude from anatmospheric tower bottoms is charged through line 10 through a filter 12wherein salts and solids are removed. The feed then passes into line 14and is heated in furnace 16 from which it passes to the first highpressure reactor 18 through line 20. The catalyst in the first stagestabilizes at a coke level of about 14 weight percent throughoutsubstantially an entire 6 month test. The effluent from reactor 18 isflashed to remove hydrogen sulfide and light hydrocarbons in flashchamber 20. These light materials pass through line 22 to line 24 andinto a recycle gas treatment apparatus 26 from which hydrogen sulfide isrecovered through line 28 and light surized stream in line 36 enters thesecond reactor 38.

Reactors l8 and 38 have the same type of low Group VI-Group VIII metalscatalyst. The effluent from the second reactor 38 in line contains about0.5 0.3 weight percent sulfur and contains all the hydrogen sulfideproduced in reactor 38. It enters the third reactor 42 through line 40without being flashed for removal of hydrogen sulfide, whereby thehydrogen partial pressure in reactor 42 is lower than the hydrogenpartial pressure in reactors 1 8 and 38. Furthermore, line 40 introducesa pressure drop between reactors 38 and 42 to further lower the hydrogenpressure in reactor 42 and so that, in terms of pressure drop, reactor42 is not equivalent to merely an elongated combination reactor 3842.Fresh hydrogen is not added to the charge to reactor 42 in order tomaintain a low hydrogen partial pressure 'in reactor 42. Reactor 42contains a catalyst comprising a higher proportion of Group /I and GroupVIII metals than the catalyst of the first two reactors and operates ata lowerpressure than does the first two reactors. If additional hydrogensulfide is required to maintain catalyst activity in reactor 42, it canbe supplicd from anextraneous source, not shown, or can be a slip-streamof hydrogen sulfide-containing low hydrogen partialpressure gases fromthe first reactor which is charged to third reactor feed line 40 throughline 23.

The coke level on the third stage catalyst stabilizes at about 20-40weight percent based on original catalyst throughout substantially anentire six month test butcontains only about 0.5 weight percent ofmetals from the feed at the end ofa 6 month test. Unless extraneoussulfur is added, the NiS catalyst can be reduced to Ni s while the M08can be reduced to M 8 The feed to the third reactor may contain a finiteamount from less than about 1 to as high as 3 weight percentasphaltenes, which is reduced to about zero percent, and clearly belowO.l weight percent asphaltenes in the third reactor depending upon thefeed to the process. The product being asphalt-free constitutes alubricating oil feedstock in a suitable boiling range without a solventdeasphalting step required. The asphaltenes have an affinity for thecatalyst sites and therefore move through the third stage at a lowerspace velocity than the lighter saturates and aromatics, which do notrequire as much desulfurization or demetallization, which lightermaterials tend to be less attracted to the catalyst sites, movingthrough the third stage at a much higher space velocity than theasphaltenes.

The effluent from reactor 42 passes through line 44 into flash chamber46 from which light gases are removed through line'48 and from whichliquid is removed through line 50. The light gases in line 48 areadmixed with the light gases in line 22 and pass to the recycle gastreatment chamber 26. Recycle hydrogen is recovered from chamber 26through line 52 and is repressurized in compressor 54 for recycle to thefeed stream through line 56 for feeding to the first'reactor 18 orthrough line 58 for charging to the second reactor 38 through heater 60.Make-up hydrogen is added through line 62. Product liquid from flashchamber 46 is passed through line 50 to a fractionator 64 from which lowsulfur, low metals, fuel oil suitable for feeding to an FCC crackingunit is removed as bottoms through line 66. If desired a separate gasoil fuel can be removed through line 68. A small amount of naphtha, ifproduced, is removed through line 70 and off-gas is removed through line72. The process converts less than 20 percent, preferably less than 10percent and most preferably less than 5 or even less than 2 percent ofthe feed in line 10 to material boiling in the naphtha range or'below.

The middle stage 38 of the three hydrodesulfurization stages of thepresent invention is pivotal to improved operation in the first stage 18and to improved operation in the third stage 42. Since the middle stage38 is a relatively high pressure stage and employs the same catalyst asthe first stage 18, it provides a combination relatively high pressureprocess with the first stage 18, wherein less catalyst is required for agiven amount of sulfur removal in high pressure stages .18 and 42, thanif the same amount of sulfur were removed in a single stage withoutintermediate flashing. This advantageous effect is the subject of Ser.No. 206,083, filed Dec. 8, 1971, now US. Pat. No. 3,775,305, which ishereby incorporated by reference. It is shown below that the cooperativeeffect between reactor 38 and the final reactor 42 causesreactor 42 toreduce catalyst consumption also. The intermediate flashing step betweenstages 1 and 2 provides the advantages necessary to high pressureoperation, i.e., removing hydrogen sulfide reaction productandincreasing hydrogen partial pressure by removal of hydrogen sulfideand light hydrocarbon gases produced in the first stage. In this mannera higher average-hydrogen partial pressure in the first two stages isrealized with consequent greater sulfur removal occurring in stages 18and 38 than would occur in a single stage with the same total quantityof catalyst or in two stages without intermediate flashing with the sametotal quantity of catalyst. The middle or second stage 38 alsocooperates with the final and relatively low pressure stage 42 utilizingthe more highly active hydrogenation catalyst by providing hydrogensulfide required in the low pressure stage by virtue of the facts thatthere is no flashing step between the second and third stages, there isno high pressure purified hydrogen injection between the second andthird stages and the line 40 between the second and third stagesintroduces a pressure drop between the stages. In this manner, thesecond stage provides hydrogen sulfide to the third stage and therebyhelps to keep the third stage catalyst in an active, sulfided state,and'also helps to reduce the hydrogen partial pressure in the gasesentering the third stage in order to advantageously lower the hydrogenpressure in the third stage.

' The third stage catalyst is more preferential to metal removal thansulfur removal as compared to the first stage catalyst. For example, thefirst stage catalyst removes weight percent of'both feed sulfur and feedmetals while the third stage catalyst removes 73 weight percent of itsfeed sulfur but 89 weight percent of its feed metals.

The low sulfur material in line 66 of FIG. 8 is charged to the FCCsystem shown in FIG. 9 through line 74 and possibly also line 76 of FIg.9. The total feed to the riser is preferably thehydrodesulfurized'residual oil but distillate can also be added to theriser, if desired. Dispersion steam isadded to the FCC riser throughlines 78 and 80. Hot regenerated zeolite catalyst is added through line82 while recycle oil is added through line.

84. All catalyst fed to the riser is fed to the riser inlet to provideas high a flash equilibrium vaporization temperature as possible at thereactor inlet to vaporize the maximum possible quantity of residue toprevent coke formation due to non-vaporization of high boiling feed oil.There is essentially no increase of catalyst to oil ratio along thereaction flow stream in the riser and there is essentially no slippageof catalyst relative to hydrocarbon along the reaction flow path. Theentire mixture passes upwardly through riser cracker 86 which is cappedat 88 and the mixture discharges from the riser through lateral slots 90into a stripper chamber 92. The residence time in the riser is less than5 seconds, preferably less than 2 or 3 seconds. Stripping steam is addedthrough line 94 to remove hydrocarbons from deactivated catalyst andcracked effluent passes through a separation chamber 96 containingcyclones, not shown, wherein solids are'removed from product

1. A PROCESS FOR PRODUCING GASOLINE FROM A FEED RESIDUAL PETROLEUM OILCONTAINING ASPHALTENES, METALS AND SULFUR WITHOUT A DISTILLATION OR ASOLVENT EXTRACTION STEP FOR REMOVAL OF ASPHALTENES COMPRISINGPRETREATING SAID FEED OIL IN A PLURALITY OF HYDRODESULFURIZATION STAGESIN SERIES INCLUDING AN INITIAL STAGE AND A FINAL STAGE EACH OPERATING ATA HYDROGEN PRESSURE ABOVE 1,000 PSI AND AT A TEMPERATURE BETWEEN ABOUT650* AND 800*F., EACH STAGE EMPLOYING A CATALYST COMPRISING GROUP VI ANDGROUP VIII METALS ON ALUMINA, THE CATALYST IN SAID FINAL STAGECOMPRISING A HIGHER WEIGHT PERCENT OF GROUP VI AND GROUP VIII METALSTHAN THE CATALYST IN SAID INITIAL STAGE, INCREASING THE TEMPERATURE INEACH STAGE WITH INCREASING CATALYST AGE TO COMPENSATE FOR CATALYSTACTIVITY AGING LOSS, MAINTAINING A LOWER HYDROGEN PRESSURE IN SAID FINALSTAGE THAN IN SAID INITIAL STAGE, REMOVING ASPHALTENES, METALS ANDSULFUR FROM THE FEED OIL IN SAID INITIAL AND SAID FINAL STAGES WITH AGREATER AMOUNT OF METALS AND SULFUR BEING REMOVED FROM THE FEED OIL INSAID INITIAL STAGE THAN IN SAID FINAL STAGE, SAID PRETREATMENTPRODUCTING A SUBSTANTIALLY ASPHALTENE-FREE HYDRODESULFURIZED EFFLUENTCOMPRISING MORE THAN 80 VOLUME PERCENT YIELD BOILING ABOVE THE GASOLINERANGE BASED ON FEED, AND CONVERTING AT LEAST A PORTION OF SAIDASPHALTENE-FREE EFFLUENT TO GASOLINE IN A ZEOLITE RISER CRACKER.
 2. Theprocess of claim 1 wherein the final temperature in said initial andfinal stages is about the same and is reached at about the same time inprocess operation.
 3. The process of claim 1 wherein saidasphaltene-free effluent comprises more than 90 volume percent boilingabove the gasoline range based on feed.
 4. The process of claim 1wherein the asphaltene-free effluent comprises more than 95 volumepercent boiling above the gasoline range based on feed.
 5. The processof claim 1 wherein the asphaltene-free effluent comprises more than 98volume percent boiling above the gasoline range based on feed.
 6. Theprocess of claim 1 wherein in said feed pretreating step section theinitial stage catalyst deactivation is due primarily to saturativemetals-loading on the catalyst and the final stage catalyst deactivationis due primarily to coke formation on the catalyst.
 7. The process ofclaim 6 wherein said saturative metals-loading occurs when the mostsaturated portion of the catalyst contains 40 to 50 weight percent ofGroup VI plus Group VIII metals plus metals deposited from the feed oil.8. The process of claim 1 wherein fuel oil and gasoline are recoveredfrom the cracked product without further desulfurization.
 9. The processof claim 1 including a hydrodesulfurization stage between said initialand final stages.